Various types of erosions such as stress corrosion cracking, fitting, intergranular corrosion, and abrasion, and also mechanical damages occur in a heat generating tube of a nuclear power station. The erosions and mechanical damages are generally divided into an axial defect and a circumferential defect. The defects occurring in the heat generating tube hinder operational safety and an economical efficiency, for example, when the defects penetrate beyond a certain thickness of the heat generating tube, a primary cooling water contaminated by radioactivity leaks into a secondary cooling water, subsequently a nuclear power plant may become contaminated. Thus, a technique which can detect the defects and can measure a degree of the defects in advance is required.
In the nuclear power station, a newly occurring defect and development of an existing defect are inspected using a nondestructive method during routine maintenance, which is performed at every period. An eddy current test using a bobbin type probe is currently used to nondestructively inspect and measure the defects occurring in the heat generating tube.
Conventionally, in the eddy current test for the heat generating tube, a side wall of the heat generating tube is initially inspected using the bobbin type probe, and a part where an abnormal condition is detected is inspected in detail using a motorized rotating pan cake (MRPC) probe. The bobbin type probe has detection speed of 1 m per second capable of performing the detection at a comparatively higher speed, however the MRPC probe has low speed of 5 mm per second. Accordingly, a considerable amount of time is required to precisely detect the part where the abnormal symptom is detected.
Also, the eddy current test using the bobbin probe has a problem in that because a circumferential defect may not be detected, there is a high probability of an error in analyzing a signal with respect to the defects since a defect signal is distorted by a magnetic phase when the magnetic phase occurs in the heat generating tube.
Thus, an apparatus which can rapidly, precisely, and easily measure the defects occurring in the heat generating tube, and a method using the apparatus are earnestly required.